Method of making a cool burning gun propellant

ABSTRACT

A COOL BURNING SINGLE BASE GUN PROPELLANT COMPOSITION COMPRISE OF A BLEND 12.6 PERCENT NITRATION LEVEL NITROCELLULOSE AND 11.0 PERCENT NITRATION LEVEL NITROCELLULOSE IN SUFFICIENT QUANTITIES TO PROVIDE AN AVERAGE NITRATION LEVEL OF 12 PERCENT AND A SOLVENT METHOD FOR THE MANUFACTURE OF SAID PROPELLANT COMPOSITION WHEREIN A SINGLE SOLVENT RATIO OF ETHER AND ALCOHOL ARE EMPLOYED IN THE COLLOIDIZATION PROCESS.

United States Patent Oflice 3,718,719 Patented Feb. 27, 1973 US. Cl.264-3 B 4 Claims ABSTRACT OF THE DISCLOSURE A cool burning single basegun propellant composition comprised of a blend 12.6 percent nitrationlevel nitrocellulose and 11.0 percent nitration level nitrocellulose insufiicient quantities to provide an average nitration level of 12percent and a solvent method for the manufacture of said propellantcomposition wherein a single solvent ratio of ether and alcohol areemployed in the colloidization process.

BACKGROUND OF THE INVENTION This invention relates generally topropellants and more particularly to gun propellant compositions andmethod of their manufacture.

It has been known for some time, that gun wear, i.e., the erosion of theinterior of the gun barrel, is caused chiefly by two factors; hightemperature of the gases formed upon ignition of the propellantcomposition and the corrosive eflect of these gases upon the metal ofthe barrel.

Prior attempts to provide gun propellant compositions which minimizethese causes of gun Wear have been somewhat successful. However, theyhave not been particularly economical and, on occasion, have createdother undesirable side effects due to the addition of ingredients whichupon ignition yield gases of discomforting odors.

Other attempts to provide less erosive cool burning gun propellantsi.e., possess low flame temperature, also have been advanced. These alsohave been somewhat uneconomical and have created other problems such asthe deposition of large quantities of carbon in the gun barrel whichthrough cumulative elfects renders the gun inoperative.

Moreover, recent efforts have been made to utilize the large quantitiesof obsolete nitrocellulose propellants in stock to avoid the largeeconomic loss that would be incurred by their non-use. Accordingly, aneed exists for a cool burning gun propellant employing this unusednitrocellulose.

SUMMARY OF THE INVENTION Accordingly, one object of this invention is toprovide a new gun propellant composition and method for its manufacture.

Another object of the present invention is to provide a cool burning gunpropellant composition.

Still another object of the instant invention is to provide aneconomical cool burning gun propellant composition.

Another object of the present invention is to provide an economical coolburning gun propellant composition which may utilize reclaimednitrocellulose.

Still another object of this invention is to provide a method for themanufacture of a new gun propellant composition which is less tediousand expensive than past processes.

These and other objects are accomplished by providing a single base gunpropellant composition comprised of two nitrocellulose grades, one beingreclaimed (reground) 12.6 percent nitrogen nitrocellulose and the otherbeing 11.0 percent nitrogen virgin nitrocellulose. Moreover, the objectsof this invention are further accomplished by a method of manufacture ofthe present gun propellant compositions comprising a solvent processwherein a single solvent ratio of a mixed solvent is capable of forminga homogenous colloid of both of these nitrocellulose grades.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The gun propellant compositionsof the instant invention are comprised of an admixture of 12.6 percentnitrogen nitrocellulose aud low grade nitrocellulose of an 11.0 percentnitrogen content. The 12.6 percent nitrogen nit-rocellulose may beeither virgin nitrocellulose or preferably, for economical purposes,reclaimed nitrocellulose. The processes of reclaiming and reworkingobsolete nitrocellulose propellants are conventional and well within theknowledge of one skilled in the art. Generally, the old nitrocelluloseis ground and pulverized and since the potential energy level remainsessentially unaltered, the whole process is basically merely aregraining procedure.

However, Whichever of the 12.6 percent nitrogen nitrocellulose isutilized, it and the virgin 11.0 percent nitrogen nitrocellulose areblended together in sufiicient quantities to provide 'a gun propellantwith an average nitration level of nitrocellulose of 12 percent.

Thus, according to the instant invention, the unexpected discovery wasmade of a cool burning and less erosive gun propellant having an averagenitration level of 12 percent by weight employing nitrocelluloses ofnitration levels differing as much as 1.6 percent, and wherein one ofthese nitrocellulose grades may be reclaimed nitrocellulose, which is atleast comparable in ballistic performance and chemical stability to apropellant made from one nitration level of nitrocellulose of 12percent.

The gun propellant compositions made in accordance With the presentinvention generally contain a large percentage of nitrocellulose, i.e.,from about 87 to about percent by weight. Of course, other ingredientsnormally employed in compositions of this nature also may be included inrelatively minor amounts. For example, inorganic salts such as potassiumsulfate and/or potassium nitrate may be incorporated as flashsuppressants from about 1 to 3 percent by weight. Stabilizers andCoolants, such as ethyl centralite and butyl stearate, may be used inamounts of about 1 percent for the centralite to amounts of from about2.5 to about -6 percent of the butyl stearate. Additionally, lubricants,such as basic lead carbonate, may be also included in about 1 percent byweight quantities of the total composition.

The process employed in the manufacture of the gun propellantcompositions of the instant invention is begun following conventionalsteps for the preparation of nitrocellulose gun propellant compositions.That is, in the instant process, as in the prior art processes, thenitrocellulose is dehydrated, if Water wet, or wrung of excess alcohol,if alcohol wet, down to a known level. Unlike prior art processes, thepresent process employs nitrocelluloses differing in nitration levels tothe extent of about 1.6 percent in quantities sufiicient to provide afinal blend of nitrocellulose characterized by an average nitrationlevel of about 12 percent.

The differing nitration level nitrocelluloses are blended and mixedtogether with some of the other dry propellant ingredients to be used,such as the potassium sulfate and the basic lead carbonate in aconventional propellant mixer. Traditionally. ethyl centralite and butylstearate are not added dry but rather in ether solution for moreoptimized mixing.

At this point, the nitrocellulose mixture is colloided employing a mixedether/alcohol solvent. It is intended that ether and alcohols refer todiethyl ether and ethyl alcohol.

It has been found in the present process that a single solvent ratio offrom about :70 to about :65 parts by weight of ether and alcohol,respectively, is sufficient to form a good colloidal mixture of the 11.0percent nitration nitrocellulose and the 12.6 percent nitrationnitrocellulose. Preferably a 32:68 parts by weight ether/ alcohol ratiois used.

In prior art process of manufacturing propellant compositions usingdifferent nitration level nitrocelluloses, each nitrocellulose requiresa separate colloiding process with a different solvent ratio therebyadding to the tediousness and expense of the process.

The quantity of solvent employed in the instant process, i.e., solventlevel, is generally from about 80 to about 90 percent by weight of thetotal composition. Preferably about an 85 percent solvent level isemployed. Any of the residual alcohol already present in thenitrocellulose and/ or ether employed in the addition of otheringredients to the composition are taken into consideration in thecalculation of the quantity level and ratio of the mixed alcohol/ethersolvent. Furthermore, adjustments of the solvent level and ratio must becommensurate with volatile losses during the mixing cycles of thecomposition.

After colloidization is complete, the remaining steps of the processfollow conventional lines. Thus, the propellant compositions is removedfrom the mixer and pressed into cylindrical blocks. These blocks ofpropellant are then strained into strands to remove any uncolloidedparticles and blocked again. The blocks are extruded into strands, thestrands are cut and then dried to a minimum or desired level of volatilecontent. In the context of this invention, volatiles is intended to meansuch things as water, alcohol and ether.

The mixing process of the instant invention may be performed at varioustemperatures depending on processing considerations as is the case withconventional procedures for mixing propellants of this nature. Forexample, a temperature of 75 F. has been found to be desirable.

The general nature of the invention having been set forth, the followingexample is presented as a specific illustration thereof. It will beunderstood that the invention is not limited to this example but issusceptible of different modifications that will be readily recognizedby one of ordinary skill in the art.

EXAMPLE lose mixture in conjunction with about 152 pounds of ethylalcohol. The total mix was agitated, at about 75 F., until a homogenouscolloid Was obtained and subsequently removed from the mixer. Thismixture was then processed in a conventional manner, i.e., the mixturewas pressed into cyclindrical blocks in a 12 inch vertical press. It wasthen strained, reblocked and extruded in the same press and cut anddried.

The solvent level used in the exemplary process was 81 percent whereinthe 12.6 percent nitration level nitrocellulose was initially alcoholWet and had a total volatiles content of about 23 percent by weight,while the 11.0 percent nitration level nitrocellulose also was initiallyalcohol wet and had a total volatiles content of about 22 percent byweight. The solvent ratio of ether to alcohol was 33:67 parts by weightand the total volatiles content of the final propellant composition wasabout 3.27 percent by Weight.

The gun propellant compositions of this invention, as exemplified by theexample, have a nominal adiabatic flame temperature in the range of fromabout 2000 K. to about 2200 K.

The composition of the example was manufactured in prototype lots ofabout 10,000 pounds and were evaluated by extensive gun firing tests in5-inch/54-caliber guns. The average muzzle velocity obtained was about2650 feet per second and the average breach internal pressure within thegun was about 20.2 tons per square inch.

Obviously, numerous modifications and variations of the presentinvention are possible in the light of the above teachings. It istherefore to be understood that within the scope of the appended claimsthe invention may be a practiced otherwise than as specificallydescribed herein.

What is claimed and desired to be secured by Letters Patent of theUnited States is:

1. A process for the manufacture of a single base gun propellantcomposition comprising the steps of:

(a) mixing a suflicient quantity of 12.6 percent nitration levelnitrocellulose with a sufficient quantity of 11.0 percent nitrationlevel nitrocellulose to provide a nitrocellulose mixture of an averagenitration level of about 12 percent,

(b) adding to and mixing with the mixture of step (a) a solvent mixtureconsisting essentially of a mixture of diethyl ether and ethyl alcoholfor a suflicient time to form a colloidal mixture therewith, whereinsaid solvent mixture is added in a sufiicient quantity to provide asolvent level of from about to about percent by weight of the totalcomposition and wherein said solvent mixture is in a ratio of from about30:70 to about 35 :65 parts by weight of diethyl ether to ethyl alcohol,and

(c) blocking, extruding and drying the product of step 2. The process ofclaim 1 wherein said solvent mixture is added in a sufiicient quantityto provide a solvent level of about 85 percent by weight of the totalcomposition and wherein said solvent mixture is in a ratio of about32:68 parts by weight of diethyl ether to ethyl alcohol.

3. The process of claim 1 wherein said 12.6 percent nitration levelnitrocellulose is reclaimed nitrocellulose.

4. The process of claim 2 wherein said 12.6 percent nitration levelnitrocellulose is reclaimed nitrocellulose.

References Cited UNITED STATES PATENTS 3,014,246 12/1961 Cook et al264---3 BX 3,116,190 12/1963 Zihlman et al. l49l00 3,317,361 5/1967Hopper et a1 149-96 X 3,473,982 10/1969 Herzog et al 149100 X BENJAMINR. PADGETT, Primary Examiner S. J. LECHERT, JR., Assistant Examiner US.Cl. X.R. 149-94, 96,

